Secondary payload interface

ABSTRACT

A secondary payload interface for payload communications using a primary payload communications channel is provided. The secondary payload interface may include a plurality of input/output couplers which may connect the primary payload communications channel to a secondary payload. The plurality of input/output couplers may establish an isolated secondary payload communications channel within the primary payload communications channel. The secondary payload interface may be designed such that control and telemetry interactions with the operators of the communications satellite are limited.

BACKGROUND OF THE INVENTION

This invention relates to a secondary payload interface that allows asecondary payload to communicate using a primary payload communicationschannel.

Communications satellites, such as geostationary (GSO) and non-GSOsatellites, are typically designed to facilitate bent-pipe transmissionof communications or processed digital data traffic from one place onEarth to another. As such, the primary payload of a communicationssatellite provides very high communications bandwidth.

Although typically built with that single purpose in mind, thesesatellites may provide platforms for secondary payloads. For example,communications satellites can provide power, thermal control, andattitude control system (ACS) functions, as well as other services, tosecondary payloads, such as, for example, earth-observing orweather-monitoring payloads. An auxiliary high rate communicationssystem can be provided on the communications satellite to accommodatethe secondary payload. However, other factors may make it difficult toimplement such a solution. For example, while the secondary payloaditself may not consume significant resources, the communicationssatellite may not be able to handle the size, weight, and/or power ofthe auxiliary communications system in addition to the secondarypayload.

SUMMARY OF THE INVENTION

In accordance with the invention, a secondary payload interface forpayload communications using a primary payload communications channel isprovided, allowing the secondary payload to borrow a portion of theprimary payload communications channel. The secondary payload interfacemay include a plurality of input/output couplers which may connect theprimary payload communications channel to a secondary payload. Theplurality of input/output couplers may include, but are not limited to,radio frequency (RF) directional couplers or power dividers, isolatedbaseband data ports, devoted RF ports, multiplexed shared buses withopen collector interfaces, open collector transistor drivers,opto-isolated data ports, switches, filters, resistive elements, or anyother type of signal interface.

In accordance with another aspect of the invention, operations of thesecondary payload are kept separate from operations of the primarypayload. For example, interruption of operations of the primary payloadshould be prevented if the secondary payload malfunctions or fails. Inaddition, if the secondary payload is a strategic asset that transmitsand receives sensitive data, the operator of the secondary payload maywant to securely control the secondary payload and secure datatransmissions to and from the secondary payload.

Therefore, in order to make the sharing arrangement acceptable tooperators of both the primary and secondary payloads, in someembodiments, the plurality of input/output couplers may establish anisolated secondary payload communications channel within the primarypayload communications channel. For example, directional couplers maycouple into a transponder path of the primary payload communicationschannel to establish the secondary payload communications channel.Likewise, a devoted port on a router in a primary payload (e.g., aprocessing payload) may be used to establish an isolated secondarypayload communications channel within the primary payload communicationschannel.

The input/output couplers (inclusive of any interface component) mayallow the secondary payload to share the communications infrastructureof the primary payload without intervention by the operations center ofthe communications satellite. Conversely, the input/output couplers mayalso ensure the reliability and continuity of the operations of theprimary payload regardless of the state of the secondary payload. Forexample, the input/output couplers may allow the primary payload to usethe rest of the primary payload communications channel while thesecondary payload is communicating with a ground station. In addition,if the secondary payload is not communicating with a ground station, theinput/output couplers may allow all of the primary payloadcommunications channel to be restored to the primary payload. Thus, evenif the secondary payload malfunctions and is no longer able tocommunicate, the primary payload may continue to communicate withoutinterruption, with full access to the primary payload communicationschannel. As yet another example, if operation of the primary payloadrequires the full bandwidth of the primary payload communicationschannel, it may be possible to reserve or recapture (e.g., using orpassing through the input/output couplers) the bandwidth available to orbeing used by the secondary payload. Use of this feature will depend onthe agreement between the operators of the primary and secondarypayloads. In the preferred implementation, the input/output couplersprovide fault resistance of the communications services of the primarypayload in the event of a failure of the secondary payload or thesecondary payload interface.

In addition to isolation of the secondary payload communicationschannel, the secondary payload interface may include encryption anddecryption modules and additional circuitry for processing data for bothdownlink and uplink data streams. For transmitting data, the circuitrymay first receive encrypted data from the encryption module. Thecircuitry may then encode and modulate the encrypted data beforeinjecting the data into the downlink data stream via the output coupler.For receiving data, the circuitry may receive data from the uplink datastream via the input coupler and demodulate and process the data beforesending it to the decryption module. After the decryption module hasdecrypted the data, the secondary payload interface may pass the data tothe secondary payload.

In some embodiments, the secondary payload interface may be designedsuch that control and telemetry interactions with the operators of theprimary payload and/or the host satellite (which may be the same ordifferent) are limited. For example, control interactions may be limitedto power connections. As another example, telemetry interactions may belimited to discrete telemetry points that provide insight into the basichealth of the secondary payload interface. As a result, the secondarypayload may still be securely controlled by its operator withoutinvolvement by the operations center of the primary payload and/or thehost satellite. This approach provides segregation of signals between anencrypted state and a non-encrypted state (e.g., a “red/black”interface) as required by some encryption systems.

Therefore, in accordance with the present invention, there is provided asecondary payload interface for secondary payload communications using aprimary payload communications channel. This interface may include aplurality of input/output couplers for connecting the primary payloadcommunications channel to a secondary payload, and circuitry forallowing the secondary payload to communicate with a ground stationusing the primary payload communications channel.

Methods for allowing communications by a secondary payload also areprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantageswill be apparent upon consideration of the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like reference characters refer to like parts throughout, and inwhich:

FIG. 1 is a representation of a communications system including acommunications satellite and ground stations in accordance with oneembodiment of the present invention;

FIG. 2 is a general block diagram of an embodiment of a secondarypayload that utilizes the primary payload communications channel and theservices of the host satellite in accordance with one embodiment of thepresent invention;

FIG. 3 is a block diagram of an embodiment of the primary payloadcommunications channel of a communications satellite, coupled with asecondary payload interface in accordance with one embodiment of thepresent invention;

FIG. 4 is a block diagram of an exemplary secondary payload interface inaccordance with one embodiment of the present invention; and

FIG. 5 is a schematic representation of a directional coupler inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Conventional communications satellites typically are dedicated toprovide a single service. Those exceptions that carry secondary payloadshave provided a dedicated, auxiliary communications system for secondarypayloads. In some cases, however, it may be desirable to add a secondarypayload to a communications satellite, but the satellite may not be ableto accommodate an auxiliary communications system because of size,weight, and/or power constraints, even though it can accommodate thesecondary payload itself.

The present invention provides a secondary payload interface forallowing secondary payload communications using the primary payloadcommunications channel. For example, the secondary payload may be anEarth-observing sensor that needs to communicate with a ground station.The secondary payload may couple into a transponder path of the primarypayload communications channel to establish a secondary payloadcommunications channel within the primary payload communicationschannel.

Because coupling into the primary payload communications channel isallowed, the need for a dedicated secondary payload communicationschannel is avoided. A secondary payload that does not require its owndedicated communications channel may be smaller, lighter, and lesscostly, and will consume less power. Moreover, if the secondary payloadis operated by a different entity than the operator of thecommunications satellite, the operator may not only charge a fee forhosting the secondary payload, but also may be able to derive additionalrevenue by charging fees for use of the primary payload communicationschannel by the secondary payload.

FIG. 1 is a representation of a communications system includingcommunications satellites and ground stations in accordance with oneembodiment of the present invention. Communications system 100 mayinclude communications satellites 102 and 112, uplink ground stations104 and 106, and downlink ground station 108 and 110. Communicationssatellite 102 may host a primary payload that broadcasts a variety ofdata received from uplink ground station 104 or by cross-link betweencommunications satellites 112 and 102. For example, the primary payloadmay provide satellite radio broadcasting of audio data received fromuplink ground station 104 to downlink ground station 108 (e.g., a mobileor fixed platform receiver). As another example, the primary payload mayprovide television data received from uplink ground station 104 todownlink ground station 108.

Uplink ground station 104 and downlink ground station 108 may becollocated or separated depending on the mission requirement.

In addition to the primary payload, communications satellite 102 mayhost a secondary payload that handles data transmission to the same or adifferent set of ground stations (e.g., ground stations 106 and 110).For example, uplink ground station 106 may be an uplink station thattransmits data (e.g., secure data) to the secondary payload oncommunications satellite 102. After receiving the data from uplinkground station 106, the secondary payload may transmit the data todownlink ground station 110 for loop-back verification of the commandsignaling. As in the case of the uplink and downlink ground stations ofthe primary payload, uplink ground station 106 and downlink groundstation 110 may be collocated or separated. In some cases, the secondarypayload may share the uplink and downlink ground stations of the primarypayload, and then filter and stream its data to another location forfurther processing.

FIGS. 2 and 3 are block diagrams of an embodiment of the primary payloadcommunications channel of communications satellite 102, coupled with asecondary payload interface in accordance with one embodiment of thepresent invention. Primary payload communications channel 200 mayinclude primary payload antenna system 202. In some embodiments, primarypayload antenna system 202 may include a reflector, which reflectsand/or collects electromagnetic waves transmitted in either directionbetween the communications satellite and ground stations.

The electromagnetic waves received at primary payload antenna system 202may be filtered by input filters 300 before being sent to widebandreceiver 302. Primary payload communications channel 200 may then sendthe data to input multiplexer 304, which may allow the data to bedistributed to payloads on the communications satellite through varioustransponder paths. A transponder may include one, and, in some cases,multiple channels as a result of data compression and multiplexing. Anyfrequency band may be used in primary payload communications system 200.

Primary payload communications channel 200 may transmit data by feedingthe data to a high power amplifier redundancy switching component ofprimary communications channel 200, which may include switch networks306 and 308 and amplifier 310. For example, the data can be fed toamplifiers 310 through switch network 210. Amplifiers 310 may includeany suitable high-power amplifiers, such as, for example, traveling wavetubes or solid-state power amplifiers. The output of amplifiers 310 maythen be applied to output multiplexer 312 through switch network 308 fortransmission to primary payload antenna system 202. 36 MHz bandwidthchannels, which are available on many commercial satellites, may beprovided for the downlink channels. After data has been received atprimary payload antenna system 202, the antenna system may transmit thedata to the ground station.

Secondary payload 218 may be coupled to primary payload communicationschannel 200 through secondary payload interface 220 (see FIG. 2).Secondary payload interface 220 may couple into the transponder pathbetween input multiplexer 304 and switch network 306. Secondary payloadinterface 220 may include any suitable number of ports (e.g., one ormore ports). By coupling into the transponder path, secondary payloadinterface 220 may establish a secondary payload communications channelwithin the existing primary payload communications channel of thecommunications satellite. The secondary payload communications channelmay allow the transmission of high-bandwidth data from secondary payload218 to a ground station using the primary payload communications channel(e.g., a commercial C-Band communications channel).

The primary components of secondary payload interface 220 may includecircuitry 314, encryption module 316, decryption module 318,payload/crypto interface unit (CIU) module 320, and input/outputcouplers 322 and 324, Optional encryption module 316, decryption module318, and CIU module 320 may be integrated in secondary payload interface220 at any suitable point depending on the security requirements of thesecondary payload. For example, encryption module 316, decryption module318, and CIU module 320 may be incorporated within circuitry 314. Asanother example, shown in FIG. 3, encryption module 316, decryptionmodule 318, and CIU module 320 may be integrated-in-line betweencircuitry 314 and secondary payload 218. Once a secondary payloadcommunications channel has been established, encryption module 316,decryption module 318, and CIU module 320 may allow the operator ofsecondary payload 218 to control secondary payload 218 and protect thedata without intervention or involvement from the operations center ofthe communications satellite.

Referring now to FIG. 4, a block diagram of an exemplary secondarypayload interface in accordance with one embodiment of the presentinvention is shown. Secondary payload interface 220 may serve as aninterface for multiple secondary payloads (e.g., secondary payloads218). It will be understood that although two secondary payloads areshown in FIG. 2 to be coupled to secondary payload interface 220, anynumber of secondary payloads, from one up to a maximum number determinedby other constraints (e.g., such as space, launch weight, and availablepower) may be coupled.

In the downlink transmission stream, secondary payloads 218 may transmitdata and clock signals to secondary payload interface 220. These dataand clock signals can be either single-ended signals or differentialsignals (e.g., low-voltage differential signals (LVDS)). In someembodiments, secondary payload interface 220 may include an encryptionmodule (e.g., encryption module 316), which may be capable of supportinga variety of data rates. For example, differential data may be encryptedby running the data at high speeds over a high bandwidth LVDS system toencryption module 316 (e.g., NSA certified Type 1 COMSEC MEU-121). Inaddition, single-ended data may be encrypted by running the data over asingle-ended system to encryption module 316. Depending on the securityrequirements of the secondary payloads, each secondary payload may haveits own encryption module or multiple secondary payloads may share asingle encryption module. In some embodiments, a CIU module (e.g., CIUmodule 320 of FIG. 3) may be used to interface with any requiredcryptographic equipment for the secondary payload (e.g., to provide“red-side” control and status).

After the data has been encrypted by encryption module 316, secondarypayload interface may send the data to circuitry 314 (e.g., a secondarypayload interface modem). Circuitry 314 may then frame, perform ForwardError Correction (FEC) and baseband encoding, and finally modulate thedata onto the carrier signal using a format compatible with the primarypayload communications channel. For example, data framing module 400 mayencode bits of data into data packets. In some embodiments, data framingmodule 400 may add transmission protocol knowledge and managementinformation associated with the primary payload communications channel.

After data has been framed into data packets, FEC encoder 402 may encodethe data packets using forward error correction (FEC). Thus, errors thatare introduced during data transmission may be corrected.

FEC of the data packets aids in improving throughput and reducing therequired transmission power of the communications satellite. As aresult, the overall demand on the power system of the communicationssatellite is decreased. Alternatively, the bit rate may be increasedwhile holding the same power level and link margin. Any suitable form ofFEC may be used to improve the system throughput and reduce powerconsumption, such as, for example, block coding, convolutional coding,concatenated coding, and turbo coding schemes.

The data packets are then sent to baseband encoder 404. Baseband encoder404 may perform any final processing or formatting of the data packetsprior to modulation. For example, baseband encoder 404 may convert thedata packets from non-return-to-zero (NRZ) to NRZ-Mark (NRZ-M) forbinary phase-shift keying (BPSK) and quadrature phase-shift keying(QPSK) ambiguity resolution. As another example, baseband encoder 404may include a commutator for offset QPSK.

After the appropriate baseband encoding has been performed on the datapackets, circuitry 314 may send the encoded data packets to modulator406. Modulator 406 may modulate the encoded data packets onto a carriersignal using any suitable means of information modulation (e.g., analogor digital) such as, for example, amplitude modulation (AM), frequencymodulation (FM), frequency-shift keying (FSK), phase modulation (PM),phase-shift keying (PSK), QPSK, quadrature amplitude modulation (QAM),ultra-wideband (UWB), or code division multiple access (CDMA).

QAM is a modulation scheme which conveys data by modulating theamplitude and phase of the in-phase (I) and quadrature (Q) components ofa carrier signal. 16-symbol QAM includes 16 constellation pointsrepresented on the I-Q plane, where each constellation point contains 4bits of information, resulting in a bit-rate spectral density of 4bps/Hz. Because each symbol is represented as a complex number,modulator 406 may convey the encoded data by modulating the amplitudeand phase of two carrier sinusoidal waves (which are 90° out of phase)with the real (I) and imaginary (Q) parts of each symbol. Modulator 406may then send the symbol with the two carriers on the same frequency.This approach is desirable because data is easily transmitted as twopulse amplitude modulation (PAM) signals on quadrature carriers, and,thus, can be easily demodulated.

Using the 36 MHz (see FIG. 3) bandwidth channels provided by the primarypayload communications channel, downlink data rates of up to 144 Mbps(Nyquist limit) may be achieved with 16-QAM. In addition, the 36 MHzbandwidth channels may support downlink data rates of up to 72 Mbps withQPSK modulation. Likewise, the 36 MHz bandwidth channels may supportdownlink data rates of up to 108 Mbps with 8PSK modulation.

Temperature compensated crystal oscillator (TCXO) 408 may providesecondary payload interface 220 with a precise frequency standard thatsupports a highly stable clock signal for a digital integrated circuit.Thus, TCXO 408 may serve as a digital clock generator. It will beunderstood that TCXO 408 may provide any reference frequency required bythe communications satellite for stability and phase noise. For example,as shown in FIG. 4, TCXO 408 may be set at 10 MHz.

In some embodiments, TCXO 408 may assist with stabilizing thefrequencies for the 16-symbol QAM of modulator 406. For example, thereference frequency provided by TCXO 408 may be sent to phase lockedloop (PLL) 410, which can generate local oscillator frequencies that aremuch higher than the reference frequency. In the example shown in FIG.4, PLL 410 may generate stable 3.78 GHz local oscillator frequenciesfrom the frequency reference provided by 10 MHz TCXO 408. The 3.78 GHzlocal oscillator frequencies may then be sent to buffer amplifier 412before being transmitted to modulator 406 for frequency stabilization.PLL 410 may derive the local oscillator frequencies using any suitableapproach, such as, for example, by frequency multiplication, directly byoscillators, by a numerically controlled oscillator, or by another meansspecified by the primary payload communications channel.

Secondary payload interface 220 may include any suitable number ofinput/output couplers for connecting the primary payload communicationschannel to secondary payload 218. For example, as shown in FIG. 4,input/output couplers 322 and 324 may be directional couplers thatcouple in and out of the transponder path of the primary payloadcommunications channel to establish a secondary payload communicationschannel within the communications channel. By coupling into the primarypayload communications channel and using the existing communicationsinfrastructure, the need for a devoted secondary payload communicationschannel is avoided.

In some embodiments, the secondary payload communications channel may beisolated from the rest of the primary payload communications channel. Asa result, the isolated secondary payload communications channel mayallow an operator to securely control secondary payload 218 via thesecondary payload communications channel. In the example shown in FIG.3, secondary payload interface 220 utilizes loose (e.g., −20 dB)input/output couplers 322 and 324 to achieve integration and isolationof the secondary payload communications channel. Persons skilled in theart will appreciate that any highly reliable implementations ofinput/output couplers may be used, such as, for example, highly reliableswitches (e.g., solid-state, electro-mechanical, or other RF or IFswitches), circulators for radio frequency/intermediate frequency(RF/IF) coupling, or open collector or highly reliable tri-state devicesor devoted ports for baseband signal coupling.

Input/output couplers 322 and 324 includes metallic conductors anddielectrics and preferably are intrinsically immune to radiation induceddegradation (e.g., they are considered “rad hard”). Thus, input/outputcouplers 322 and 324 may be expected to operate reliably in the harshradiation environments of geosynchronous satellites. Conversely,electronic switches (e.g., mechanical switch matrices and pin diodes)can be vulnerable to radiation induced effects such as single-eventeffects, single event latchups, and total ionizing dose effects and/ormechanical failure due to contamination or breakage. Such degradationmay compromise or catastrophically degrade the performance of theseelectronic switches and, as a result, may compromise the viability ofthe primary payload communications channel and payload missions for boththe primary and secondary payloads. Furthermore, electronic switches arealso unreliable because the switches may fail to either open or close.In some cases, the electronic switches may even operate in indeterminatestates (both closed or both open). Input/output couplers 322 and 324,however, include no moving parts or mechanical switches, and thereforeoperate more reliably.

FIG. 5 shows how a coupler may appropriately configure two adjacenttransmission lines to achieve isolation. The characteristics of coupler500 may be determined by its geometrical and/or structuralconfiguration. Coupler 500 separates signals based on the direction ofsignal propagation. For example, some portion of signal flowing intoinput port 502 appears at coupled port 504. Similarly, some portion ofsignal flowing into coupled port 504 is fully coupled to input port 502.However, coupled port 504 and output port 506 are isolated such that anysignal flowing into output port 506 will not appear at coupled port 504but will be fully coupled to input port 502. In the configuration shownin FIG. 5, isolated port 508 is terminated with a matched load.

Referring back to FIG. 4, the functionality of couplers for isolatingthe secondary payload communications channel will now be discussed. Onthe downlink side, a portion of the power for the data packets that arebeing transmitted to output coupler 322 (e.g., coupled port 504 of FIG.5) will appear at the output channel (e.g., input port 502 of FIG. 5).In particular, because in this example output coupler 322 has a couplingloss of −20 dB, 1% of the input power will appear at the output channel.Data being fed into output coupler 322 (e.g., output port 506 of FIG.5), however, will be isolated from circuitry 314. Similarly, on theuplink side, a portion of the power for the data received from the inputchannel of input coupler 324 (e.g., input port 502) will appear atcircuitry 314 (e.g., coupled port 504). However, the coupled port ofinput coupler 324 will be isolated from the output port. The combinationof input/output couplers 322 and 324 creates an isolated secondarypayload communications channel. In addition, the output is isolated fromthe input which reduces self-interference to the uplink from thedownlink. The ability to isolate control of and output from secondarypayloads 218 from the operators of the primary payload may be important,especially if the secondary payloads are strategic assets.

In addition, because this coupling implementation has no net reliabilityimpact on the communications services of the primary payload, thisimplementation represents a robust approach to ensuring reliability andcontinuity of the mission of the primary payload. For example, the loosecoupling enables the primary payload to use the rest of the primarypayload communications channel (e.g., any bandwidth not utilized bysecondary payload 218) while secondary payload 218 is communicating withthe ground station. Thus, if the secondary payload only utilizes afraction of the primary payload communications channel with its uplinkand downlink, the remainder of the channel may be utilized by a primaryservice end user. As another example, the loose coupling of input/outputcouplers 322 and 324 may enable the primary payload to use all of theprimary payload communications channel when secondary payload 218 is notcommunicating with the ground station (e.g., the lack of communicationmay be due to either planned termination or unplanned malfunction orfailure). Thus, when secondary payload interface 220 is powered off,normal traffic may resume in the transponder path of the primary payloadcommunications channel, and full capacity may be returned to the primarypayload. As yet another example, in response to determining that theprimary payload requires additional bandwidth that is currently beingused by or available to secondary payloads 218, secondary payloadinterface 220 (e.g., using input/output couplers 322 and 324) maydisable communications of the secondary payloads to reserve or recapturethe full bandwidth of the primary communications channel. Use of thisfeature will depend on the agreements between the operators of theprimary and secondary payloads, but the feature may be technicallysupported.

Referring now to the uplink stream, after data has been received fromthe secondary payload communications channel via input coupler 324,circuitry 314 may demodulate, process, and decode the coupled signal.Because in this example input coupler 324 has a coupling loss of −20 dB,a very small portion of the input power (1%) will appear at circuitry314. Thus, low-noise amplifier (LNA) 414 in circuitry 314 may be used toamplify the power of the received data. LNA 414 is an active componentthat is capable of boosting the power while adding as little noise anddistortion as possible. In addition, LNA 414 will not damage thetransponder path of the primary payload communications channel.

The amplified signal will then be fed to vector demodulator 416. Forgeneralized I/Q de-modulation, vector demodulator 416 may multiply thesignal with orthogonal signal components (e.g. sine and cosine) toproduce two baseband signals (e.g., I(t) and Q(t)). Because frequencyvariations due to temperature or aging may be introduced in thefrequency translation process, a stable oscillator is desired. Thisreference may be provided by the stable 3.78 GHz local oscillatorfrequencies received from PLL 410 and amplified by buffer amplifier 418.

Circuitry 314 may then send both I(t) and Q(t) to band-pass filter (BPF)420 and BPF 422. BPFs 420 and 422 may then process I(t) and Q(t) suchthat frequency terms outside of a certain frequency range are removedand components that are in phase (or in quadrature) are extracted. AfterI(t) and Q(t) have been filtered, I(t) may be passed through analog todigital (A/D) converter 424, and Q(t) may be passed through A/Dconverter 426. Finally, I(t) and Q(t) may be merged and demodulated bydemodulator 428. Demodulator 428 may use any suitable demodulationscheme complementary to the modulation scheme used by modulator 406,such as, for example, QPSK, QAM, PSK, etc. Circuitry 314 may then sendthe demodulated data to baseband decoder 430, which can perform theopposite operation of baseband encoder 404.

Decryption module 318 (e.g., a MCU-110 decryptor) may receive thedecoded data, and perform decryption so that the data can be routed tosecondary payload 218. If uplink data rates are approximately at 1 Mbps,an RS-422 bus (shown in FIG. 3) may provide the interface betweendecryption module 318 and secondary payload 218. Similar to encryptionmodule 316, persons skilled in the art will appreciate that, dependingon the security requirements of the secondary payloads, each secondarypayload may have its own decryption module or multiple secondarypayloads may share a single decryption module.

In some embodiments, secondary payload interface 220 may be designedsuch that control and telemetry interactions with the operators of thecommunications satellite are limited (e.g., host satellite services 230of FIG. 2). For example, control interactions with the communicationssatellite may be limited to connections that provide power to secondarypayload interface 220. As shown in FIG. 4, the Vsupply connectionenables power to be provided to power supply 432. In addition, theVreturn may provide a power control signal for the communicationssatellite. As another example, telemetry interactions with thecommunications satellite may be limited to discrete telemetry pointsthat provide insight into the basic health of secondary payloadinterface 220. Suitable telemetry points may include but are not limitedto, for example, carrier lock (e.g., U/L carrier lock), bit lock (e.g.,U/L bit lock), decrypt lock (e.g., U/L decrypt lock), temperature,heartbeat, and frame lock. Opto-isolator status module 434 may providethese telemetry points to communications satellite.

The bandwidth requirements for continuous control and telemetryinteractions between secondary payload interface 220 and thecommunications satellite may vary depending on the required data rate.For example, for a data rate of 2.0 Mbps, the bandwidth requirement isdependent on the bit-rate spectral density of the implemented modulationschema. A portion of the channel bandwidth provided by the primarypayload communications channel may thus be used to support the uplinkchannels. As a result of this design, although some of the operations ofsecondary payloads 218 (e.g., control and telemetry interactions) areconnected to the communications services of the communicationssatellite, the secondary payload may still be securely controlled by theoperator of the secondary payload without involvement by the operationscenter of the communications satellite. Persons skilled in the art willappreciate that secondary payload interface 220 may be expanded into anypayload-to-communications systems interface where the secondary payloadmay utilize a fraction or all of a communications channel shared byother services.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that the invention can be practiced byother than the described embodiments, which are presented for purposesof illustration and not of limitation, and the present invention islimited only by the claims which follow.

1. A secondary payload interface for secondary payload communicationsusing a primary payload communications channel. 2-37. (canceled)